This invention relates to semiconductor circuit manufacturing and more particularly to a system and method for determining a center of a wafer on a wafer table.
Semiconductor manufacturing includes the process of moving semiconductor substrate dies from a wafer table to a lead frame after they have been cut from a silicon wafer of substrate material. A silicon wafer is first placed on an adhesive surface and is cut into rectangular dies. After cutting, the adhesive surface is placed on a wafer table of a die bonder apparatus. The die bonder deposits an adhesive on the lead frame, removes a cut die from the adhesive surface, and places it on the lead frame. The silicon wafer from which the dies are cut is round, such that there will be some dies that are not fully rectangular. These non-rectangular dies will be left on the adhesive surface and discarded.
If the process of removing dies from a silicon wafer is automated, the position of the silicon wafer and dies must be known or estimated, in order to allow a robot arm to manipulate the wafer and dies. Nevertheless, the position of the silicon wafer may randomly change with respect to the known coordinates of the adhesive surface during the die cutting operation. When such random changes occur, no die may be present at some locations in which a die is expected. This condition may result in unnecessary wafer table movements.
To prevent this condition from occurring, known methods of automating the removal of cut dies of a silicon wafer from the adhesive surface typically include conservative assumptions about the location of the wafer on the adhesive surface. These assumptions may result in a loss of usable cut dies, or the performance of additional wafer table movements that increase the amount of time needed to remove the cut dies.
Therefore, it is a general object of the present invention to provide a system and method for finding the center of a silicon wafer on a wafer table that substantially eliminates or reduces the problems associated with removing cut dies from a wafer table that result from uncertainty of the wafer""s location.
In particular, a system and method for finding the center of a silicon wafer on a wafer table is described that may be used to precisely locate the wafer, to prevent unnecessary wafer table movements during the die removal process, and to minimize or prevent waste of usable cut dies.
According to one embodiment of the present invention, a method for determining the center of a silicon wafer on a wafer table is provided. The method includes receiving silicon wafer data from a sensor. The silicon wafer data is received at a wafer center computing system. The coordinates of the wafer center (Xw,Yw) in a wafer table Cartesian coordinate system are computed. The location of the silicon wafer edge is then determined from the wafer center coordinates (Xw,Yw) and the known silicon wafer diameter.
One important technical advantage of the present invention is that the center of a silicon wafer on a wafer table may be precisely located. The position of the silicon wafer edge on the wafer table can then also be precisely located with respect to the center of the silicon wafer.
Another important technical advantage of the present invention is that die removal methods may be implemented that minimize the number of usable cut dies that may be lost during the die removal process.